Some 28,000 years ago in what is now the British territory of Gibraltar, a group of Neandertals eked out a living along the rocky Mediterranean coast. They were quite possibly the last of their kind. Elsewhere in Europe and western Asia, Neandertals had disappeared thousands of years earlier, after having ruled for more than 200,000 years. The Iberian Peninsula, with its comparatively mild climate and rich array of animals and plants, seems to have been the final stronghold. Soon, however, the Gibraltar population, too, would die out, leaving behind only a smattering of their stone tools and the charred remnants of their campfires.

Ever since the discovery of the first Neandertal fossil in 1856, scientists have debated the place of these bygone humans on the family tree and what became of them. For decades two competing theories have dominated the discourse. One holds that Neandertals were an archaic variant of our own species, Homo sapiens, that evolved into or was assimilated by the anatomically modern European population. The other posits that the Neandertals were a separate species, H. neanderthalensis, that modern humans swiftly extirpated on entering the archaic hominid's territory.